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Earnings per share (Details) (USD $)
In Thousands, except Share data, unless otherwise specified
 3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Earnings Per Share [Abstract]    
Net income (loss) $ 73,779us-gaap_NetIncomeLoss $ (20,104)us-gaap_NetIncomeLoss
Amount allocated to common stockholders (in hundredths) 91.91%cenx_NetIncomePercentageAllocatedToCommonShareholders [1] 100.00%cenx_NetIncomePercentageAllocatedToCommonShareholders [1]
Basic EPS:    
Net income (loss) allocated to common stockholders 67,813us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic (20,104)us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic
Net income (loss) allocated to common stockholders - (in Shares) 88,814,000us-gaap_WeightedAverageNumberOfSharesOutstandingBasic 88,717,000us-gaap_WeightedAverageNumberOfSharesOutstandingBasic
Earnings Per Share, Basic (in dollars per share) $ 0.76us-gaap_EarningsPerShareBasic $ (0.23)us-gaap_EarningsPerShareBasic
Effect of Dilutive Securities:    
Share-based compensation plans 0us-gaap_DilutiveSecuritiesEffectOnBasicEarningsPerShareOther 0us-gaap_DilutiveSecuritiesEffectOnBasicEarningsPerShareOther
Share-based compensation plans - (in Shares) 555,000us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements 0us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements
Diluted EPS:    
Net income (loss) allocated to common stockholders with assumed conversion $ 67,813us-gaap_NetIncomeLossAvailableToCommonStockholdersDiluted $ (20,104)us-gaap_NetIncomeLossAvailableToCommonStockholdersDiluted
Net income (loss) allocated to common stockholders with assumed conversion - (in Shares) 89,369,000us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding 88,717,000us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding
Earnings Per Share, Diluted (in dollars per share) $ 0.76us-gaap_EarningsPerShareDiluted $ (0.23)us-gaap_EarningsPerShareDiluted
Stock Options [Member]    
Securities Excluded from Computation of Earnings Per Share [Line Items]    
Securities excluded from calculation of diluted EPS (in shares) 333,266us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
/ us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis
= us-gaap_EmployeeStockOptionMember		 [2] 603,032us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
/ us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis
= us-gaap_EmployeeStockOptionMember		 [2]
Service-based share awards [Member]    
Securities Excluded from Computation of Earnings Per Share [Line Items]    
Securities excluded from calculation of diluted EPS (in shares) 0us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
/ us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis
= us-gaap_RestrictedStockUnitsRSUMember		 [2] 442,456us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
/ us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis
= us-gaap_RestrictedStockUnitsRSUMember		 [2]
[1] We have not allocated net losses between common and preferred stockholders, as the holders of our preferred shares do not have a contractual obligation to share in the loss.
[2] In periods when we report a net loss, all share awards are excluded from the calculation of diluted weighted average shares outstanding because of their antidilutive effect on earnings (loss) per share. In periods when we report net income, certain option awards may be excluded from the calculation of diluted EPS if the exercise price of the option award was greater than the average market price of the underlying common stock.